Method of design and manufacture of laminated orthodontic brackets

ABSTRACT

A design and manufacturing process uses flat sheets with outline shapes cut into the metal to manufacture orthodontic parts in laminate form. These sheets are aligned and stacked together, tack welded and brazed together in a flat form or may be bent together and then brazed. The process may be used to produce either commonly used conventional orthodontic brackets or very complicated shapes required for difficult applications.

BACKGROUND OF THE INVENTION

This invention relates to the fabrication of detailed dental appliancesand more particularly to a method of designing and making orthodonticbrackets and the like.

Heretofore, orthodontic brackets have customarily been made by diestamping, machining or casting. As the orthodontic art has progressed,the desire to make more intricate and smaller parts has been limited bythe available materials and methods of fabrication.

In the past, gold was the material of choice for orthodontic brackets,but now stainless steel is usually used. The 300 series stainless steelsare the most common materials selected for orthodontic attachments.Sometimes 17/7 and 17/4 stainless steels are used because these steelscan be heat treated.

The tooling for stamped parts is expensive, but once it is built, theparts can be made relatively accurately and inexpensively. Stamping andforming requires the use of softer metals but this limitation can beovercome by using heat treatable metal such as 17/7 stainless steel inthe annealed state. The part is then heat treated. Holes in stampedparts must be no smaller than the material thickness. In general, themore complex the parts, the more impractical die stamping and formingbecomes.

Job shops that can make shapes in flat stock are readily available, butthe stamping and metal folding needed to make complicated orthodonticattachments requires special manufacturing skills. At the present time,use of die stamping and forming is limited to flat parts such as lockpins and mesh foil bonding pads and to the manufacture of simple formedbrackets for the Begg light wire technique and for some buccal tubes.

Metal machining is commonly used in the manufacture of orthodonticparts. Semi-soft, machineable grades of 300 series stainless are thepreferred materials. Parts made from machineable grade stainless steelcannot be heat treated. Since these parts must remain semi-soft,strength becomes a problem in the manufacture of small cross sections.

Some orthodontic attachments such as a simple lingual button (FIG. 1)can be made on a screw machine. Screw machine job shops are readilyavailable. Set up charges for a screw machine operation are inexpensive,but the cost per part is expensive. As the shapes of attachments becomemore innovative and complex and less available in the common job shop,the complicated tooling becomes very expensive.

The introduction of the lost wax investment casting process in themanufacture of orthodontic attachments has allowed parts to be designedthat could not be made by die stamping and forming or by machiningtechnologies. Wildman's Edgelok bracket (U.S. Pat. No. 3,780,437) issuch an example. Orthodontic brackets made by the investment castingmethod begin as plastic patterns formed by injection molding. Very oftenthis is high density polystyrene. The injection molds in which thesepatterns are formed are expensive to make but produce very accurateparts. Very intricate shapes can be produced. The investment process istime consuming and the cost per part is high. All parts are fullyannealed as cast and are soft. If strength is needed, a heat treatablestainless such as 17/4 can be used. Investment casting to the tolerancesrequired in the manufacture of orthodontic parts is very exacting and isnot readily available from commercial job shops.

Sinter bonded powered metal is used in an injection mold and is a viablealternative to casting. A cost advantage in sinter bonding comes fromthe elimination of the investment step. Nonetheless, the molds mustwithstand the wear problem of molding the powered metal and are veryexpensive. Casting limits the design of brackets to shapes and crosssectional dimensions that can be reliably cast without voids and withsufficient strength for orthodontic applications.

Conventionally, bracket bodies are fabricated separately and thenmounted as a discrete step on a mesh-foil bonding pad. This is typicallydone by spot-welding or by brazing with various solders, including 80-20gold-copper and 82-18 gold-silver eutectics applied in wire or pasteform.

The tendency in the art is to move toward automatic and releasablebrackets and to applications, such as lingual orthodontics, that requirea wider variety of part configurations. The increased complexitychallenges the limits of casting techniques and materials. And, togetherwith the need for many different parts, it makes the cost of manufactureprohibitive. It would be desirable for orthodontists to be able to haveparts made on a custom or semi-custom basis. Clearly, however, the costand complexity of making state-of-the-art orthodontic parts by currentmethods precludes having parts made locally.

Chemical etching, which is sometimes called chemical milling, is a metalforming technology that is known and used in other arts. Chemicalmilling is used extensively in the production of flat stainless steelparts and is readily available from commercial job shops. It is alsoused in the electronics industry for making printed circuit boards. Inthis process, a photographic tool or mask is made from a line drawingand an acid resistant layer is printed on a sheet of metal. When thesheet is dipped in an acid bath, the imprinted pattern is resolved inthe acid, leaving untouched the metal that is protected by the resistantfilm. This process is relatively cheap. Very intricate complicatedshapes can easily be produced. Hard materials can be shaped by chemicaletching. By staggering the pattern of the printed resistant film, someareas can be etched on one side but not on the other. Chemical etchingis limited to relatively thin flat stock.

In its conventional form, chemical etching is unsuited for makingorthodontic attachments other than such things as lock pins made fromflat stock. Accordingly, a need remains for a better process for makingorthodontic brackets.

SUMMARY OF THE INVENTION

One object, therefore, is to improve and simplify the design andfabrication of orthodontic appliances.

A second object of the invention is to enable economical construction ofcomplicated shapes of metal orthodontic brackets.

Another object is to reduce the tooling costs and per unit costs ffabricating new orthodontic bracket designs.

Yet another object is to enable reduction of feature dimensions (forexample, cross-sectional dimensions and holes) and/or gross size ofmetal orthodontic brackets.

A further object is to avoid the dimensional and materials limitationsof conventional methods of making orthodontic parts.

An additional object is to enhance the design options for orthodonticparts, particularly to make smaller, more versatile orthodonticbrackets.

My invention is a design and manufacturing process for the production ofmetal orthodontic attachments and the like. This method includesdefining a three dimensional shape of an orthodontic bracket having abase, a body and an attachment member formed in said body and segmentingthe designed shape of the bracket along a plurality of spaced-apartsurfaces to define at least two laminae. Each lamina has a thicknessdefining one dimension of the bracket body in accordance with thespacing of the surfaces and a peripheral edge face defining a seconddimension of the bracket body. Two layers of metal, each having twoopposite major surfaces and a thickness proportional to the spacing of acorresponding one of the laminae, are patterned with a boundary on eachlayer of metal corresponding to the peripheral edge face of thecorresponding lamina in the design. Each of the layers of metal aresectioned along the patterned boundary to form layer components,preferably by chemical etching, so that each layer component has athickness and a peripheral edge face matching the thickness andperipheral edge face of the corresponding lamina in the design. Thelayer components are assembled in accordance with the segmented shape ofthe bracket design. Their major surfaces are positioned in contactingrelationship and their peripheral edge faces in the same relativealignment as the edge faces of the laminae in the segmented shape of thebracket design. Then the assembled layer components are fused together,and preferably simultaneously to the base or bonding pad, at interfacesof said major surfaces.

The fusing step preferably includes applying, preferably by plating, abrazable metal layer, such as gold-copper eutectic, to major surfaces ofthe layer components prior to assembly and brazing the layers togetherafter assembly.

Using chemical etching for the patterning and sectioning steps includesmasking an area of at least one major surface of each layer of metalwithin said boundary and selectively chemical etching away metal fromthe layer in areas exposed around the masked areas. Either or both majorsurfaces of the layer can be masked within selected portions of a layerso that the metal within said portions remains unetched or one side canbe left exposed to half-etch such portion.

The laminae formed by segmenting the shape of the bracket body and thelayers of metal used in fabrication of the bracket can be flatthroughout all steps or can be curved, by forming the metal layersduring or following the sectioning step. Preferably, the layers of metalare patterned and sectioned in strips or sheets, each comprising aplurality of replicated layer components interconnected by runners.Indexing holes can be formed in the runners of successive layers andused for aligning the components for assembly by inserting an indexingpin through the indexing hole of each layer.

The foregoing method provides great freedom of design and inexpensivemanufacture of orthodontic brackets without substantial tooling cost. Anindividual orthodontist, or a group of like-minded orthodontists such asa study club, could design and inexpensively manufacture virtually anydesired attachment. The design and manufacturing process requires noequipment or process that is not readily commercially available.Commercial job shops are available in most larger cities to performchemical etching, plating, tooling of an assembly welding fixtures andvacuum brazing. The price of creating a part with this process would bewithin the resources of an orthodontist or at least a small group oforthodontists.

The foregoing and additional objects features and advantages of theinvention will become more readily apparent from the following detaileddescription which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a prior art screw-machined orthodonticcleat.

FIG. 2 is a perspective view of an orthodontic cleat designed andfabricated by the method of the present invention.

FIG. 3 is a perspective view of an intermediate step in the assemblyprocess used to make a plurality of the cleats of FIG. 3.2.

FIG. 4 is a plan view of a portion of the assembly of FIG. 3 positionedin a welding assembly fixture.

FIG. 5 is a cross-sectional view taken along lines 5--5 in FIG. 4showing the electric spotwelding step of the assembly process.

FIG. 6 is a perspective view of the assembled parts after the weldingstep of FIG. 5 and a subsequent vacuum-brazing step.

FIG. 7 is a perspective view of a prior art machined siamese edgewiseorthodontic bracket.

FIG. 8 is a perspective view of a siamese edgewise bracket designed andfabricated by the method of the present invention.

FIGS. 9A, 9B and 9C are side (mesial-distal), front (labial) and top(inciso-occlusal) views of the bracket of FIG. 8.

FIGS. 10A and 10B are plan views of the layer components of the bracketof FIG. 8 shown in a flat condition in an intermediate step of theassembly process.

FIG. 11 is a cross sectional view taken along lines 11--11 in FIG. 9B,showing the bracket parts after forming the layer components,preparatory to spot-welding the parts to the pad.

FIG. 12 is a third example showing additional orthodontic appliancestructures that can be made by the invention.

DETAILED DESCRIPTION General Description of Method

In this process, the shape of the attachment is designed so that two ormore stacked layers determine the shape of the part. The sum of thethickness of the layers determines a dimension of the part perpendicularto the layers. The other two dimensions of the part are determined bythe outline shape of each individual layer which are formedindependently. The layers are aligned, one layer to another, andpositioned precisely in a welding assembly fixture, and tack welded andthen brazed in a vacuum or hydrogen atmosphere. The brazed layers becomeone laminated part. In the simplest form of the method, the layers areallowed to remain flat. In more advanced applications, the layers can bebent or formed before brazing to produce a greater variety of shapes.

Die stamping and photochemical etching are suitable ways to form outlineshapes in flat stock. In high volume, parts are made cheaply usingstamping, but die stamp tooling is relatively expensive. Chemicaletching is the preferred embodiment in many cases. Almost any shape thatcan be drafted on paper can be reproduced as a finished metal layer. Thetooling is very inexpensive. Additional architecture can be incorporatedby etching one side only in selected regions, producing depressions thatare half the thickness of the stock.

When a part is designed so the components of the part consist of flatlayers, both the design and manufacture of orthodontic parts become verysimple. As the designer outlines the part, he slices the elements of thepart into flat or curved layers. The design proceeds to a drawing ofeach layer which is conveniently 20× actual size. Chemical milling jobshops that will turn these drawings into flat metal parts are readilyavailable. The cost of this operation is inexpensive. Preferably, forease of later process economic production of many parts, each layercomponents of a single part is replicated many times in a sheet of flatstock. This is conveniently done by conventional photo-reproductiontechniques.

The next step is to plate onto the formed flat layers first a very thin(e.g., on the order of a few microns) layer of copper and then a verythin layer of gold. The preferred ratio of the thickness of the layersis 20% copper to 80% gold by molecular weight. The metal forms aneutectic braze which is used at a later step in the process to fuse thelayers together.

The next step is to assemble the layers in an assembly welding fixture.This fixture can be assembled by commercial tool makers. The electrodesof such fixture can be arranged to fit into a spot welder of the typethat most orthodontists own.

Brazing is done preferably in a vacuum atmosphere without flux by acommercial vacuum brazer. After brazing, the assembled parts areseparated from one another along their respective outlines. The partscan then be tumbled and would be ready to use.

In disclosing the details of this method, two examples are used. Thefirst example is a lingual button. A screw-machined conventional lingualbutton (FIG. 1) is redesigned by my new method and will look like thedrawing in FIG. 2 after manufacturing. The component parts of thelingual button 20 are the base 24 and the elastic retaining button 22.The screw-machined base and button are brazed to a mesh 28 foil pad 26.The detailed description shows how the base 24 and button 27 componentsare converted to layers

The second example is a common machined twin wing edgewise bracket (FIG.7) which is redesigned and manufactured by the new method. It will looklike the drawing in FIG. 8. Example 2 shows how the layers are formed inthe dimension of their thickness as well as peripherally, so that theywill nest together before brazing. The method can thereby form a newversion of the twin wing edgewise bracket. The new version 91 can bemuch stronger and smaller than the machined 90 form because it can bemade of heat treated 17/7 stainless steel

EXAMPLE 1

FIG. 2 shows a lingual cleat 21 designed and manufactured by the methodof the invention. This lingual cleat 21 is analogous to the commonlyused lingual button 20 made on a screw machine. The lingual cleatconsists of a common orthodontic mesh 28 and foil 26 bonding pad andthree layer components 32, 34, 36 designed so that when they are brazedtogether at interfaces 42, 44 and to the top surface 40 of pad 26 atinterface 46, they form a complete part. The two layer components 32, 34next to the pad become the base 25 of the lingual cleat 21 and areanalogous to the base 24 of the lingual button 20. The third layercomponent 36 forms an elastic, oblong retaining member 23 which is moreuseful than circular button 22 of the common screw machine lingualbutton 20.

FIG. 3 shows a projection view of the layer components as they would beoriented just prior to insertion in an assembly fixture. Each of thethree layer components 32, 34, 36 are connected to like components withrunners 60, 62, 64 so the parts can be processed in continuous strips,increasing manufacturing economy. The runners contain index holes 66,68, 70 to receive index pins 72 of an assembly welding fixture, shown inFIG. 4 and FIG. 5. The runners of each layer are connected to thecomponents 32, 34, 36 by a constricted notch 54, 56, 58 in the runner.These notches have the thinnest width in the runner strip and act as abreakoff point when the parts and the runners are separated. Regions 53,55, 57 in FIG. 2 indicate the breakoff points in the finished part afterdetachment of the runners.

The layer components are ultimately fused by gold and copper eutecticbraze plated on the strips, but first they must be assembled in properorientation and tack welded together preparatory to brazing The assemblywelding tool (FIG. 4 and FIG. 5) is made from a block 74 of suitableplastic such as Delrin. A relative non-conductor of electricity must beused so that current can flow from the welder electrodes 78, 80 directlythrough the components to be welded. For the breakoff system to workwell, the pads 26, 28 must be fixtured separately without runners so thepad foil 26 will braze to the body parts 32, 34, 36 and not to therunner system 60, 62, 64. Therefore, a pocket 76 is designed in the base74 of the welding assembly fixture that is configured to receive thepads in a slightly convex-concave condition and to hold the pad inproper orientation with the convex foil side 26 facing the three layers.The bottom of the pad pocket 77 contains a hole 79 slightly smaller thanthe size of the pad. This hole accepts one electrode 80 of an electricspot welder.

The block 74 of the welding assembly tool is fitted with indexing pins72 to maintain orientation of the layers. The three layers 32, 34, 36are then inserted into the fixture with the use of the index pins 72which fit into the indexing holes 66, 68, 70 of the layers. The two bodylayers 34, 36, which are identical in this example, are inserted firstand then the lingual cleat layer 32 is inserted into the fixture withthe index pins inserted into the indexing holes. A small piece of brazeor solder 47 is inserted into the hole formed by aligning the threeholes 48, 50, 52 in the layer components of the part in each of thethree layers.

An electric spot welding machine is used to join the fixed components. Abase electrode 80 is then inserted into the base pad electrode hole 79.The opposing electrode 78 is inserted into the solder hole 48 of theelastic retaining cleat layer 36. The electrode 78 applies pressure,forcing the layers together, and is then activated to spot weld thelayer components of the part into place. The welding electrode pressureand the welding current should be adjusted so that the gold braze 47 inthe solder hole 48, 50, 52 is retained in the hole with the flash andmetal distortion of the weld. An alternative method is to place thesolder into the hole just before brazing. The weld should be strongenough to hold the pad and the three layers in proper orientation duringbrazing.

The brazing operation is done in a hydrogen atmosphere or preferably ina vacuum atmosphere. Job shops that provide this service are readilyavailable.

To facilitate brazing the pad and the layers should be plated prior toassembly first with copper and then with gold. The proportionatethickness of the copper and gold plated layers should be 20% copper and80% gold by molecular weight. Standard plating procedures as outlined inTable 1 are preferable.

                  TABLE 1                                                         ______________________________________                                        PLATING                                                                       Process Step    Chemical     Concentration                                    ______________________________________                                        1.   Solvent degrease                                                         2.   Anodic electroclean                                                                          Oakite 90    8-12 oz/gal                                       (for 2-3 min.)              40-60 lbs                                    3.   Rinse-clean                                                                   (cold running water)                                                     4.   Cathodic electro-                                                                            Muriatic Acid                                                                              50% 40 gal                                        activate 50% H.C.L.                                                           and 50% water for                                                             30-60 sec.                                                               5.   Rinse-clean                                                                   (cold running water)                                                     6.   Alkaline cyanide                                                                             Copper Cyanide                                                                             3-4 oz/gal                                        copper plate for            30-40 lbs                                         10-25 sec. at 5-15                                                                           Sodium Cyanide                                                                             3.5-4.25 oz/gal                                   amps per square foot        35-50 lbs                                         to obtain .000004-                                                                           Roplex Cu    2-4% by vol                                       .000010" thickness          3.2-6.4 gal                                                      Sodium       3.0-4.0 oz/gal                                                   Carbonate    35-45 lbs                                    7.   Rinse-clean                                                                   (cold running water)                                                     8.   Acid gold plate 60-90                                                                        Potassium Gold                                                                             .44-.73 Toz/gal                                   sec. at 5-10 amps                                                                            Cyanide      6.5 Toz                                           per square foot to                                                                           Potassium    4.8-8.0 oz/gal                                    obtain .000012-                                                                              Citrate      4.5 lbs                                           .000016" thickness                                                                           Citric Acid  2.8 lbs                                                          Ni Brightner .8-.9 gm/liter                                                                342 mls                                                          Mono K       10 oz/gal                                                        Phosphate    5.6 lbs                                      9.   Rinse-clean                                                                   (cold running water)                                                     10.  Dry and pack                                                             ______________________________________                                    

The gold braze added to the solder hole 48, 50, 52 should also be 80%gold and 20% copper braze. Plating the layer components and pad forbrazing assures that all contacting surfaces are wetted with braze. Thiscan be enhanced by adding braze adjacent the interface of the layers andprovides a reservoir of braze that is wicked into the interface areas.

The mesh 28 and foil 26 pads would preferably be die stamped to shapebecause chemically milling the mesh material is difficult and the shapeof the pad is quite simple. The layer components 32, 34, 36 might be diestamped but would preferably be chemically milled because tooling costswould be much less expensive for these complex parts. Die stamping ofsimple shapes and chemical milling are both technologies readilyavailable in job shops.

EXAMPLE 2

The design and manufacturing process may be used not only to makeorthodontic attachments of simple shapes like the lingual cleat justdescribed, but also more complicated shapes such as a twin wingedbracket. FIG. 8 shows a conventional twin wing edgewise bracket 90manufactured by machining.

A twin wing edgewise bracket contains two sets of tie wings 92 separatedby a space 93. The tie wings provide a tie area 101. The tie wings areattached to the main body of the bracket 96 which contains an arch wireslot 94 which accepts an arch wire 95 (FIG. 9A, 9B, 9C).

FIGS. 9A, 9B and 9C show a twin wing edgewise bracket 91 designed andmanufactured by the new design and manufacturing method described here.Both the machined bracket and the new method bracket are gold brazed toa conventional bonding pad 98 which has mesh 100 that is diffusionbonded to the pad.

The design and manufacturing process for the twin winged bracket 91 isessentially the same as has been described for the fabrication of thelingual cleat 21 with two additional steps. The layer components areformed to define the arch-wire slot and wings and half etched to provideadditional architecture. The flat layers are chemically milled to thedesigned shapes of layer components 102, 104 shown in FIG. 10A and FIG.10B. Then the layer components are formed in the dimension of theirthickness so that the inside layers 104 can nest in the outside layer102 forming the archwire slot 94 and the body of the bracket 96 and therecurved wings 92. One or more layer components may be designed so thata portion of the metal is etched off of a given area to half thethickness of the layers in the chemical milling process. In makingbracket 91, region 106 of layer 104 was half-etched to form the tie areain the wing 101 of the twin bracket 91. Half etching was also used toprint identification marks 108 on the wing 92 of the bracket.

The welding assembly fixture shown in FIG. 11 is similar to the fixtureused in Example 1. It consists of a plastic block 116 with a pad pocket118 that receives the pad 98. The pad pocket has a receptacle 119 for anelectrode 114 from a spot welder 114. The upper electrode 112 isconfigured to fit into the arch wire slot 94 of the formed part 102. Theformed part then fits into the outside layer 104 and is held against thepad by the pressure of the electrodes as may be seen in FIG. 11. Thesame runner strip and indexing system could be used for this part as wasused in Example 1.

After the parts are welded they are vacuum brazed in the same way as theparts in Example 1. The strength of the braze joint between layercomponent 104 and the foil layer 98 can be enhanced by wrapping a thinwire of the braze (8020 AuCu) around the interface of such layers beforevacuum brazing.

By changing the angle of the electrodes, different slot angles in thebase can be created.

Having illustrated and described the principles of my invention by wayof two examples, it should be apparent that the invention may bemodified in arrangement and detail and can be applied to a wide range oforthodontic appliances, without departing from such principles. FIG. 12shows additional useful structures that can be formed in accordance withthe invention. A rectangular hole 120 is formed by half-etching opposingfaces of two layers to form opposed depressions or channels 128, 130. Alarger hole 122 can be formed by combining half-etching a slot 126 inone layer and forming the other layer to create an opposing slot 124. Ashoulder-type configuration can be made by folding a margin 132 of onelayer around an edge 134 of the other layer. A slot 136 is formedbetween the edge of the wrapped margin 132 and the side of formed region124. I claim all embodiments and modifications falling within the scopeand spirit of the following claims.

I claim:
 1. A method of designing and fabricating orthodontic brackets, comprising:defining a three dimensional shape of an orthodontic bracket having a base, a body and an attachment member formed in said body; segmenting the shape of the bracket along a plurality of spaced-apart surfaces defining at least two laminae, each lamina having a thickness defining one dimension of the bracket body in accordance with the spacing of the surfaces and a peripheral edge face defining a second dimension of the bracket body; providing at least two layers of metal, each having two opposite major surfaces and a thickness proportional to the spacing of a corresponding one of the laminae; patterning a boundary onto each layer of metal in accordance with the peripheral edge face of the corresponding lamina; sectioning each of the layers of metal along the patterned boundary to form layer components, each layer component having a thickness and a peripheral edge face matching the thickness and peripheral edge face of the corresponding lamina; assembling the layer components in accordance with the segmented shape of the bracket, with their major surfaces in contacting relationship and with their peripheral edge faces in the same relative alignment as the edge faces of the laminae in the segmented shape of the bracket; fusing the assembled layer components together along said major surfaces; and patterning and sectioning steps including masking an area of at least one major surface of each layer of metal within said boundary and selectively chemical etching away metal from the layer in areas exposed around the masked areas.
 2. A method according to claim 1 in which the fusing step includes applying a brazable metal layer of a composition suited to orthodontics to major surfaces of the layer components prior to assembly and brazing said layers together after assembly.
 3. A method according to claim 2 in which the layers of metal are stainless steel layers and the brazable metal layer is a gold eutectic layer.
 4. A method according to claim 2 in which the step of applying a brazable metal includes plating 20% copper and 80% gold by molecular weight onto the layer components.
 5. A method according to claim 1 in which both major surfaces of at least one layer are masked within selected portions of the area within said boundary so that the metal within said portions remains unetched.
 6. A method according to claim 1 in which only one major surface of the layer is masked within a selected portion of the area within said boundary and the opposite major surface remains unmasked within said portion so that the metal within said portion is half-etched to reduce the thickness of the resultant layer component in said portion.
 7. A method according to claim 1 in which the laminae formed by segmenting the shape of the bracket body and the layers of metal used in fabrication of the bracket are flat.
 8. A method according to claim 1 in which the laminae formed by segmenting the shape of the bracket body include at least one lamina that is curved, the layer of metal corresponding to the curved lamina is flat when patterned and is then formed to a curve.
 9. A method according to claim 8 in which at least two of the laminae are curved along a common surface and the corresponding layer components are formed so that their opposed major surfaces are likewise curved.
 10. A method according to claim 1 in which each of the layers of metal are patterned and sectioned in strips or sheets, each comprising a plurality of replicated layer components interconnected by runners.
 11. A method according to claim 10 including forming indexing holes in the runners of successive layers and aligning the components for assembly by inserting an indexing pin through the indexing hole of each layer.
 12. A method according to claim 10 including forming the runners with a first cross-sectional area and forming breakoff points of a second cross-sectional area less than the first cross-sectional area adjacent the peripheral edge face of each layer component.
 13. A method according to claim 10 in which the base of each bracket is a bonding pad, including forming the bonding pads as discrete pads, forming each bonding pad to provide a convex upper surface so that the runners remain disconnected from the pad, and forming the runners with breakoff points such that the runners readily detach from the component layer.
 14. A method according to claim 1 including forming solder holes in the successive layer components, assembling the layer components with the solder holes aligned, and inserting and melting solder in the aligned solder holes.
 15. A method according to claim 1 in which the assembly step includes assembling the layer components on a foil-mesh bonding pad and fusing the layer components together and to an upper surface of the pad.
 16. A method according to claim 15 in which the fusing step includes applying a brazable to the major surfaces of the layer components and to the upper surface of the pad prior to assembly and brazing said layers and pad together after assembly. 